Re: Powering a relay

On Thu, 15 Sep 2005 03:03:46 +0200, "petrus bitbyter"
<pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx> wrote:

>"Captain Dondo" <yan@xxxxxxxxxxxxxxxx> schreef in bericht
>news:11ih7dl4arbm9e9@xxxxxxxxxxxxxxxxxxxxx
>> OK, I have a real basic question....
>>
>> I have an embedded computer. It had digital I/O. Per the manufacturer,
>> "When the DIO pins are configured as outputs, they can source 4 mA or sink
>> 8 mA and have logic swings between 3.3V and ground."
>>
>> OK, I prefer to work as source. So... How do I get 4 ma @ 3.3V to
>> control a 5V relay that needs 100 ma to operate?
>>
>> ISTR something about transistors, but it's been a few years since my
>> electronics classes....
>>
>> Right now I need to be able to power LEDs, but eventually I need to siwtch
>> 120 VAC and 24-48 VDC at a few amps load, and I thought I could use relays
>> for that. But this has thrown a wrench into the works....
>>
>> Any suggestions?
>>
>> Thanks,
>>
>> --Yan
>
>Yan,
>
>A transistor solution shown below. The NPN are general purpose transistors
>like BC547. Don't forget the diode otherwise your transistor will be blown.
>An 1N4148 or similar will do. A much simpler solution is using a FET.
>A BSS295 or similar will do.
>
>
> +---+----+------+5V -+-----+-
> | | | | |
> | - _|_ | |
> .-. ^ |_/_|- - _|_
> | | | | ^ |_/_|-
> 330| | +----+ | |
> '-' | | |
> | | +-----+
> | |/ |
> +------| NPN |
> | |> |
> | | |-+
> ___ |/ | ----->| BSS295
> -|___|--| NPN | |-+
> 5k6 |> | |
> | | |
> | | |
> ----------+--------+-------- --------+-----
> GND
>created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
>
>
>petrus bitbyter

I think the OP was asking that when the I/O is _sourcing_ 4mA, that
this is when the relay should be turned on. I may have misunderstood,
though.

Jon
.

Relevant Pages

  • Re: Powering a relay
    ... It had digital I/O. ... Don't forget the diode otherwise your transistor will be blown. ... this is when the relay should be turned on. ... The transistor solution shown above inverts the output signal which might not be wanted. ...
    (sci.electronics.basics)
  • Re: Powering a relay
    ... > "When the DIO pins are configured as outputs, they can source 4 mA or sink ... > control a 5V relay that needs 100 ma to operate? ... A transistor solution shown below. ... The NPN are general purpose transistors ...
    (sci.electronics.basics)
  • Re: Powering a relay
    ... Per the manufacturer, "When the DIO pins are configured as outputs, they can source 4 mA or sink ... control a 5V relay that needs 100 ma to operate? ... ISTR something about transistors, but it's been a few years since my electronics classes.... ... A transistor solution shown below. ...
    (sci.electronics.basics)
  • Re: doubling up on a coil transistor?
    ... those transistors of the coil's inrush current and less soldering ... to add snubbers to the relay contacts. ... transistor will have a slightly lower base-emitter voltage, ...
    (rec.games.pinball)
  • Re: inrush current
    ... resistor so it acts as a Schmidt trigger and avoids relay chatter. ... transistor completes the line up of only 3 transistors, ... I have a circuit in use which is sensitive to relay chatter, ...
    (sci.electronics.repair)